Barium-induced effects on structure and properties of β-Ca3(PO4)2-type Ca9Bi(VO4)7

Ca9–xBaxBi(VO4)7 (0 ≤ x ≤ 1.5) solid solutions with the β-Ca3(PO4)2-type structure were prepared by a solid-state method. Powder X-ray diffraction study of 0 ≤ x ≤ 0.7 showed that Bi3+ and Ba2+ cations were completely incorporated into the β-TCP-type host framework up to x = 0.7. Ca9-xBaxBi(VO4)7 (x = 0.25, 0.5) structures were refined by the Rietveld method using powder synchrotron X-ray diffraction data. DSC, SHG and dielectric properties measurements of Ca9-xBaxBi(VO4) (x = 0, 0.25, 0.5) revealed two reversible first-order phase transitions (PT1 and PT2). Increase of Ba2+ content in Ca9-xBaxBi(VO4)7 leads to lowering PT1 and PT2 phase transitions temperatures due to the increase of cell volume and the structure looseness. Nonlinear optical activity of Ca9–xBaxBi(VO4)7 reaches its maximum response at x = 0.5. The amount of (M1–(M3)–M2) dipoles in Ca9–xBaxBi(VO4)7 (0